Current power technology on mobile diesel hydraulic gantry cranes employs a diesel engine running at constant speed to drive one or more hydraulic pumps that are used to drive accessories powered by the engine. These pumps supply pressurized hydraulic fluid to various hydraulic actuators, which in turn operate various crane functions such as hoist, trolley, and drive. Controlling the magnitude and direction of the hydraulic fluid flow rate to the various crane hydraulic actuators controls the magnitude and direction of the crane function. This control of the hydraulic flow rate is currently accomplished by a number of methods including direct electrical control of the displacement of a variable displacement hydraulic pump, and electric proportional control of a pump flow rate using proportional direction control valves with fixed displacement pumps or variable displacement pumps. This can entail operating a function control and depressing the crane drive pedal at the same time.
The current practice of running the engine at a constant high speed while operating the crane has several disadvantages such as: (a) high engine speed even when there is little or no flow demand; (b) higher total fuel consumption due to constant high engine speed; and (c) higher total noise due to high engine speed. Each of these practices has disadvantages in that they increase operating costs by using excess fuel, increase engine wear by operating unnecessarily at higher speeds, and increase noise pollution and, consequently, operator fatigue. For these reasons, a method for controlling an engine such that the engine provided the necessary power only when it was demanded by the operator would be an important improvement in the art.